In both 2002 and the 2003, automatic stations were
deployed on an ice floe near the North Pole and started recording
and telemetering data in May, with the ice floe drifting on similar
paths toward Spitsbergen. Instruments
included short-wave and long-wave radiometers for down-welling radiation,
air temperature, wind direction and velocity, atmospheric pressure,
ice temperature, and ocean temperature and salinity to 250 m depth.

In addition to the above mentioned instruments, the
field teams installed Web
Cameras to show the installations and some scenery. These "web
cams" collected and transmitted images throughout the entire
summer, from the beginning of snow melt to freeze-up in autumn and
the onset of darkness.

Difficulty of Summertime Observations at the North
Pole

To appreciate the value of these data and images we
should bear in mind that the proverbial "inaccessibility of
the frozen Arctic Ocean" due to cold and darkness applies to
the mild summer even more than to the cold and dark winter. During
the long and mild days of summer melt snow and ice, the surface
becomes littered with ponds and potholes, and the transportation
of people and equipment is limited to the most difficult and expensive
modes, i.e. helicopters and ice-breaking ships. It is for these
reasons that all-year manned drifting ice stations, and hence summertime
data, have been at a premium in the history of US arctic research.
While the Soviet Union maintained 30 such stations between 1952
and 1991, the US scientists were able to acquire only four sets
of summer data, two from the International Geophysical Year 1957
and 1958, one year from the Arctic Ice Dynamics Joint Experiment
in 1975, and one year from SHEBA in 1998.

Observations from the North Pole in summer 2002

The recently recorded data from automatic buoys and
web cams represent a large, and very inexpensively obtained, increment
of information about summer conditions in the central Arctic.

Fig. 2 Late July
2002 at the NPEO drifting station. The onset of surface melting
is exceptionally late.

The onset of melting usually occurs in early June,
when the temperature reaches 0°C and the surface layer turns
into a constant-temperature ice bath. In 2002, the temperature record
shows an abrupt warming to about 0°C, on 24 May, suggesting
an early arrival of the melt season. The warming event coincides
with about a week of low short-wave (250 Wm-2) and high
long-wave (300 Wm-2) down-welling radiation, which are
typical of low overcast conditions. The web cam pictures of that
period confirm the overcast. Both radiation and temperature values
remained in the normal range for the rest of the summer, and freeze-up
occurred as usual in the last week of August. Based on the early
warming event in May, one may have expected an early onset of surface
melting. Contrary to that expectation, the web cams show that it
was not until late July 2002 when the snow cover took on a soggy
appearance and isolated melt ponds appeared on the surface (Fig.2).

For the rest of the summer, the web cam pictures show
only insignificant melt pond coverage until the deposition of new
snow in late August. The pictures clearly show that snow from the
preceding winter survived the entire summer, and we must assume
that there was no, or very little, ice ablation at the surface.

Soviet (Russian) records suggest a small probability
of an all-summer snow cover. But none of the U.S. ice camps experienced
a persistent summer snow. In light of recent news about global warming
and polar amplification, the all-summer snow cover of 2002 is clearly
unexpected.

Observations from the North Pole in summer
2003

Like the summer of 2002, the subsequent summer of 2003
also shows a somewhat belated (end of June) appearance of melt ponds
but, by the first week of July, pond coverage was wide spread (Fig.
3).

Unexpectedly, toward the end of July, pond coverage
decreased markedly (Fig. 4) while radiation and air temperatures
were still at their normal summer values. A possible explanation
is that the ice had become sufficiently porous for the melt water
ponds to drain by percolation.

However, in mid-August the melt ponds re-appeared (Fig.
5), putting in question the hypothetical pond drainage by percolation.

Fig. 3
On 4 July 2003, melt pond coverage was wide spread.

Fig.4 On
25 July 2003, the melt water pond coverage diminished, suggesting
that the ponds may have drained by percolation.

Fig. 5
On August 14 2003, after about a half month of little pond coverage,
surface melting appears to have resumed, covering large areas
with melt water.

The melt ponds shown in Fig.5 remained unfrozen until
the end of the month. During the first days of September they were
covered by new snow (Fig. 6).

Fig. 6 In the first
week of September 2003, melt ponds were covered by new snow.

The preceding samples illustrate
the extraordinary value of the web cam pictures. This technology
has clearly produced a large amount of information at a very low
cost and the current project is only a beginning. Fish-eye lens
cameras pointing to the zenith can be employed to observe cloud
amount. A camera could be used to measure accumulation/ablation
by taking pictures of suitably marked stakes, a method that would
yield more representative values than those from a sonic device
that looks at a single point. Cameras could also be used to take
pictures of radiometers and other instruments to determine whether
their readings are compromised by rime deposition. A persistent
difficulty appears to be the anchoring of structures in such a way
that they survive the summer melt season in their original position.
The summer snow of 2002 prevented the vertical instrument supports
from melting out but, at the end of the 2003 summer, the instrument
supports were severely tilted. This can be avoided by the use of
suitable materials to retard or avoid melting around objects implanted
in the ice.

Conclusions

The extent and thickness of the ice, and their seasonal
and secular variations, are manifest in the amount of thermal energy
exchanged in the melting and freezing of the ice. The intrinsic
difficulty is that the net amount of heat available for freezing
or melting is a small difference between large quantities, primarily
the incoming and outgoing streams of solar and infrared radiation.
The seasonal cycle of the heat balance responsible for the annual
thickness cycle of multi-year ice is relatively large. Good estimates
of these seasonal cycles have been established by many field studies
over the past half-century.

However, in light of increasing evidence for a secular
shift toward a warming climate and a thinning and shrinking sea
ice cover, we need to explain these changes in terms of the year-to-year
changes of the surface heat balance. Even with the most sophisticated
instrumentation and constant attention by observers in situ, these
changes have proved to be very difficult to document. Measurements
of the individual components of the heat balance have an error of
about one per cent, and we need to know the composite, net heat
balance to about the same accuracy.

The large difference between the summers of 2002 and
2003 may prove to be serendipitous. Perhaps a thorough analysis
of the recorded data for will render a quantitative explanation
for the striking difference between the two summers. But even if
this should prove infeasible, all data, whether they pertain to
the atmosphere or the ocean or the ice, are valuable in their own
right, and it remains true that every additional year of observations
during the summer represents a large addition to the existing data
base.